If your Miyoo Mini(Plus) buttons don't respond properly, this can often be fixed by cleaning the contacts

This applies to the D-PAD and face buttons.

You'll want some isopropanol (isopropyl alcohol) - at least 90%, preferably 99% - and some cotton buds. Find yourself a good tear-down video, such as https://youtu.be/INJOfsl9FNA I recommend using your fingernail or a plastic spudger to separate the two halves of the shell (you'll see from the video that it has a few clips) rather than prizing it apart the way he does.

Take your time. Don't force anything. The battery connector can be tricky.

Soak one end of the cotton bud in the isopropanol and use it to gently clean the metal contacts. Also clean the magnets in the rubber membranes. You can use the other end of the cotton bud to dry things off.

Reassemble just as carefully.